CVE-2018-5114 in Firefox
Summary
by MITRE
If an existing cookie is changed to be "HttpOnly" while a document is open, the original value remains accessible through script until that document is closed. Network requests correctly use the changed HttpOnly cookie. This vulnerability affects Firefox < 58.
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Analysis
by VulDB Data Team • 07/20/2024
This vulnerability in Firefox versions prior to 58 represents a critical security flaw related to cookie handling and script accessibility that violates fundamental web security principles. The issue occurs when an existing cookie is modified to have the HttpOnly flag while a document is already open in the browser, creating a temporal inconsistency between the cookie's actual state and its accessibility to client-side scripts. The HttpOnly flag is designed to prevent cross-site scripting attacks by ensuring that cookies cannot be accessed through client-side scripts, but this vulnerability allows scripts to continue accessing the original cookie value even after the flag has been applied. This creates a window of opportunity for malicious scripts to potentially exploit the cookie data before the document is closed, undermining the security protections that HttpOnly cookies are meant to provide.
The technical nature of this flaw stems from Firefox's implementation of cookie management within active browser sessions. When a cookie is modified to include the HttpOnly flag, the browser should immediately revoke script access to that cookie's value regardless of whether the document is open or closed. However, the vulnerability demonstrates a race condition or state management issue where the browser maintains the original cookie value in memory for scripts while simultaneously updating the cookie's attributes in the underlying cookie store. This inconsistency affects how the browser handles cookie data during document lifecycle events and reveals a failure in proper state synchronization between the cookie management system and the script execution environment. The vulnerability specifically impacts the timing of when cookie attributes are enforced versus when script access is revoked, creating a security gap that can be exploited by malicious actors.
The operational impact of this vulnerability extends beyond simple cookie access restrictions and presents significant risks to web application security. Attackers could potentially leverage this flaw to extract sensitive session data or authentication tokens that should be protected by the HttpOnly flag, particularly in scenarios where web applications rely on this security mechanism to defend against XSS attacks. The vulnerability is particularly concerning in environments where users maintain long-running browser sessions or where applications frequently modify cookie attributes during active user sessions. Network requests correctly use the updated HttpOnly cookie, meaning that while the server-side cookie handling works properly, the client-side script access remains compromised. This creates a scenario where legitimate network requests are secured but the client-side script environment remains vulnerable, potentially allowing attackers to harvest sensitive information before the document is closed and the cookie state is properly synchronized.
Mitigation strategies for this vulnerability require immediate patching of affected Firefox versions to 58 or later, where the implementation has been corrected to properly enforce HttpOnly cookie restrictions regardless of document state. Security practitioners should also implement additional monitoring and logging of cookie attribute changes within web applications to detect potential exploitation attempts. The vulnerability aligns with CWE-116, which addresses improper encoding or escaping of output, and relates to ATT&CK technique T1059.007 for script-based attacks. Organizations should conduct thorough security assessments of their web applications to ensure that cookie handling practices are properly implemented and that no reliance is placed on the HttpOnly flag in vulnerable browser versions. Regular security updates and patch management processes should be prioritized to prevent exploitation of similar timing-based vulnerabilities in browser implementations.